Trichinella spiralis

Owen, 1835

The genus Trichinella (trichinae) in the worm class of nematodes, contains as the most important human pathological species Trichinella spiralis and Trichinella britovi, both causative agents of trichinosis (trichinellosis), which, however, is now rare in Central Europe due to trichinella testing. In Eastern Europe (Bulgaria, Serbia) and Greece (Dimzas D et al. 2019) smaller outbreaks have been recorded repeatedly in the past (Vutova K et al. 2020; Pavic S et al. 2020), where both species could be detected equally. Apparently, deliberate "alternative" pig husbandry played a role in these outbreaks. In tropical areas, trichinella is not of great importance.

In principle, all mammals are susceptible, but natural infections are most likely in carnivores and omnivores such as the fox and the pig. In Central Europe, the red fox is considered the most important reservoir of the pathogen. In Germany and Switzerland, human infection is notifiable.

After ingestion of meat containing Trichinella, the larvae are released in the stomach by digestive enzymes (e.g. pepsin) and mature into adult worms in epithelial cells of the upper small intestine within a few days. After mating, the males die relatively quickly. Females begin depositing larvae as early as 4 to 7 days after infection. This usually occurs over 2 to 4 weeks, but can last up to 3 months. In total, a female releases about 500 to 1,500 larvae. This "enteric phase" usually lasts about 20 days. During this time, colonization of the intestinal epithelium leads to the signs of an "acute intestinal infection" with nausea, vomiting, diarrhea, and others.

The young larvae pass through the mucosa and enter the bloodstream, where they circulate and finally migrate into the striated muscles. Oxygen-rich muscles, i.e. muscles with a good blood supply, such as the diaphragm, neck, chewing muscles, muscles of the shoulder girdle and the upper arms are preferentially attacked. During active invasion, muscle fibres are destroyed.

After 2 to 3 days, the Trichinella larvae reach their final intracellular location near the fascia. Within 4 to 6 weeks, the infected muscle cell is transformed into a capsule-shaped "Ammen cell" in which the larvae can survive for up to 30 years. The larvae, which have grown to about 1 mm in length, are coiled in a spiral. After a period of about 6 months to over a year, calcification begins, first of the parasite capsule and only much later of the parasite itself (information from the RKI). Even through the calcified capsule, a metabolic exchange of the trichinella with the surrounding tissue could be proven.

Trichinellosis is a foodborne disease resulting from the consumption of raw or insufficiently heated meat containing Trichinella larvae (trichinella, trichinae). The clinical course depends on the number of Trichinella larvae incorporated. It begins with the signs of food poisoning. As few as 50 larvae can cause significant clinical signs. In the case of a larger number of larvae, significant systemic reactions occur within 24 hours after ingestion, such as fever, intestinal colic, diarrhoea and muscle pain. Furthermore, edema of the face (eyelid edema), macular exanthema, subungual splinter hemorrhages are found.

Laboratory confirmation of Trichinella infection is primarily by antibody detection (by ELISA or immunoblot), which can usually be performed early, but in some cases does not show a positive result until the 3rd or 4th week of illness.

Histological examination (hematoxilin-eosin (HE) stain) of muscle biopsy specimens (from deltoid, pectoral, or biceps muscles) is less commonly practiced. The Trichinella species is determined by multiplex PCR.

Albendazole (e.g. Eskazole Filmtbl.) 10-15 mg/kg bw daily in 2 daily doses or Mebendazole (Vermox Tbl.) 200-400 mg 3 times/day for 3 days, then 400-500 mg 3 times/day for 10 days. Caveat. Side effects, therefore follow exact dosage instructions!

To prevent possible secondary symptoms of the disease, concomitant therapy with 20-60 mg prednisone (e.g. Decortin Tbl.), initial, high-dose parenteral administration of up to 1 g if complications are imminent.

1. Cortes-Blanco M et al. (2002) Outbreak of trichinellosis in Caceres, Spain, December 2001-February 2002 Euro Surveill 7: 136-138.
2. Dimzas D et al. (2019) Human trichinellosis caused by Trichinella britovi in Greece, and literature review. J Helminthol 94:e33
3. Holstein A et al. (1999) Father and son with muscle pain and loss of muscle strength. Acute trichinosis. Internist 40: 673-677
4. Liu M et al (2002) Trichinellosis in China: epidemiology and control. Trends Parasitol 18: 553-556
5. Owen R (1835) Description of a microscopic entozoon infesting the muscles of the human body. London Med Gaz 16: 125-127
6. Pavic S et al (2020) Trichinella britovi outbreak: Epidemiological, clinical, and biological features. Med Mal Infect 50:520-524.
7. Roy SL (2003) Trichinellosis surveillance--United States, 1997-2001. MMWR Surveill Summ 52: 1-8.
8. Virchow R (1859) Recherches sur le developpement de la trichina spiralis (ce ver devient adulte dans l'intestin du chien). CR Seanc Acad Sci 49: 660-662
9. Vutova K et al. (2020) Clinical and epidemiological descriptions from trichinellosis outbreaks in Bulgaria. Exp Parasitol 212:107874.
10. Zenker FA (1860) Ueber die Trichinen-krankheit des Menschen. Arch Pathol Anat Physiol Klin Med 18: 561-572.